The proposed investigation has a set of substantive and methodological goals. Substantively, it is a study of the incidence of certified cases of psychiatric disorder in 16th and 17th century England. The records of legal incompetency hearings constitute the major documentary basis of this project. These records, representing referrals to the Court of Wards and Liveries, (1540-1660), the only national institution in pre-industrial England concerned with the protection of the mentally ill, permit an analysis of fluctuations in the size, social class, sex, age, geographic and diagnostic composition of cases of possible and of certified psychiatric disorder over a hundred-year period. The contributions of institutional, political and socioeconomic factors to these fluctuations will be examined. Suggestive estimates of rates of psychiatric disorder among English landowners in specific counties will also be attempted. In addition, the reports of insanity hearings will provide some information regarding the theories held by the examining commissioners and the jury regarding the etiology of psychiatric disorder, while information on the persons making referrals will provide insight into social and familial responses to deviant behavior. Methodologically, the study aims to assess the value of a biostatistical technique of estimating the size of an original historical population based on extant incomplete lists of population members. The technique, while widely used in work on animal censuses and in some epidemiological investigations, is almost unknown in historical epidemiology and medical and social history.